Although Latinos represent one of the fastest-growing populations entering substance use disorder (SUD) treatment, they are the most likely to lack health insurance and receive disparate care in terms of treatment access, quality, and outcomes. In particular, Mexican Americans represent the largest population of uninsured and critically underserved ethnic minority individuals in the United States. As such, it is not surprisng that the Institute of Medicine (IOM) and other federal institutions have called for systematic collection of health care data on specific Latino subgroups10 to define vulnerable subpopulations, identify determinants of disparities, and prepare the health care system to develop solutions to promote health equities. The lack of representative datasets with an adequate number of Mexican Americans and information on provider quality of care to accurately explore and identify health care disparities has represented a key barrier to greater knowledge regarding strategies to improve Mexican Americans' treatment outcomes.5 Thus, using a multilevel and multiyear dataset, which includes data collected from 101 outpatient SUD treatment programs and 14,610 clients in 2011 and 2013, we will seek to detect IOM-defined disparities in terms of client achievement of 30- day sobriety at successful treatment completion. Guided by Kilbourne, Switzer, Hyman, Crowley-Matoka, and Fine's (2006) conceptual framework for advancing health disparities research, and consistent with the National Institute for Health and Clinical Excellence's (NICE) conceptual framework for public health,15 we will examine these disparities at both the individual and program level. Aim 1 will focus on detection of treatment disparities between Mexican-Americans and non-Latino Whites and Aim 2 will focus on understanding the extent to which key organizational factors (e.g., acceptance of public insurance, delivery of evidence-based treatment [EBT], and delivery of culturally and linguistically appropriate services [CLAS]) may help in the reduction of these treatment disparities. Aim 3 seeks to expand upon the NICE conceptual framework by testing the extent to which increases in programs' acceptance of public insurance (i.e., Medicaid), which will expand as part of the ACA and mostly affect Latinos in Los Angeles County, may lead to improvements in quality of care (i.e., delivery of EBT and CLAS). The proposed analysis of existing data represents a timely and cost-efficient opportunity to have a large overall impact on Latino health care disparities research and policy, especially given the innovative aspect of the proposed research is to detect, understand and reduce client- and program- level disparities for Mexican Americans, who constitute the largest Latino subgroup in the United States. Finally, given the increasing focus on health care reform and its consequences (both positive and negative), the proposed study is believed to have the potential for high overall impact because it will be one of the first known studies to examine the extent to which increases in acceptance of public health insurance, which is a key component of the ACA, lead to increases in quality of care in community-based SUD treatment.